Since an electrical or electronic device is made of different housing components, it is possible for each of the housing components to meet different requirements individually. Such a device often has a cost-benefit advantage over a device which contains just one housing component, because in the latter case either the one housing component always has to be designed to compromise between different requirements, which is technically disadvantageous, or an approach which attempts to meet all the different requirements renders the housing component too expensive to produce. Realizing the device using a plurality of housing components makes it possible to eliminate these disadvantages, in particular in the case of complex devices such as, for example, inverters designed for operation outdoors. Conversely, however, stringent requirements have to be met both in respect of IP protection and in respect of reducing interference radiation between interconnected housing components. On the one hand, therefore, the IP-sealing action and the EMC shielding should be influenced as little as possible even if the boundary-surface distances fluctuate in relation to one another. At the same time, a corresponding seal should be easy to produce and should be capable of being installed straightforwardly in the device.
In the case of an electrical or electronic device which has a plurality of housing components, a seal of the type mentioned above is inserted, for example, between two boundary surfaces which are assigned to the respective housing components. In its installed state, the seal provides IP protection, and protects the interior of the device against the ingress of foreign bodies and/or water. Foreign bodies can be understood to mean, for example, particles of dust. It is likewise the case, however, that the protection against the ingress of foreign bodies also covers protection against contact, which prevents contact being made with live, or current-carrying, components in the interior of the device during operation of the latter. At the same time, however, a low-impedance electrical connection between the housing components means that this seal also provides an EMC-shielding action at the boundary surfaces of the relevant housing components. On the one hand, therefore, the seal reduces the amount of electromagnetic interference escaping from the interior of the device into the surroundings. On the other hand, it prevents the formation, between the housing components, of a potential difference which fluctuates over time, as a result of which the housing components would act as an antenna and would emit electromagnetic interference, in an undesirable manner, into the surroundings.
The IP code assigned to the IP (International Protection or also Ingress Protection) protection usually denotes the IP protection class—and, in addition, also a permitted area of use—of an electrical device. The IP code here is made up of two digits, of which the first classifies the protection against the ingress of a foreign body and the second classifies the protection against the ingress of water. In the case of both digits, the protective action increases in each case as the value of the digit increases.
Elastomer seals are known to provide the IP protection between housing components, said seals being installed between boundary surfaces of adjacent housing components and being compressed in their installed state. The elastic properties of the seals allow the latter to compensate for housing unevennesses up to a certain degree and the compression of the seals prevents dirt and/or water from penetrating into the interior of the device. However, such seals provide just an IP-sealing action, but not an EMC shielding action at the boundary surfaces.
As far as EMC shielding is concerned, on the other hand, it is known to use metallic contact springs. The contact springs can be mounted on a boundary surface of a housing component. In the installed state, when said housing component is connected to the other housing component, the contact springs provide one or more electrical contacts between the two housing components and thus reduce the amount of electromagnetic interference escaping from the device into the surroundings. A multiplicity of such contact springs are often mounted along a relevant boundary surface of a housing component. Such EMC shielding, however, does not provide any IP-sealing action for the interconnected housing components.
In addition, so-called combined seals (cf. for example, product overview flyer from Micro Tech Components GmbH, http://www.mtc.de/sites/default/files/linkables/flyer_ihv.pdf) are also known, and these provide both IP protection and EMC-shielding action in combination. Such a combined seal has a core material made of an elastomer, wherein the core material is sheathed to some extent by metal mesh or a metal foil. The elastic properties of the core material provides for the IP protection, while the outer metal mesh in contact with the metallic housing components, or the boundary surfaces thereof, provides an electrical connection between the boundary surfaces, and therefore the EMC-shielding action. However, the metal-mesh or metal-foil sheathing applied around the outside of the core reduces IP-sealing action of the core material, for which reason such as a seal is not designed to provide high-grade IP protection, in particular IP protection in classes IP-4X, IP-5X or IP-6X. In the case of the metal mesh, this is due to the fact that the metal mesh gives rise to additional unevennesses on the surface of the seals—at least over part of the surface of the seal. If part of the surface of the seal is sheathed with a metal foil, then, on account of the metal foil being less elastic, this part is not capable—or is at least is less capable—of compensating for unevennesses on the boundary surfaces, as a result of which the IP-sealing action of the combined seal is impaired. For a similar reason, such a combined seal is also capable only to a limited extent of compensating for fluctuations in the distance between the boundary surfaces and/or unevennesses in the boundary surfaces.